Lubricating oil additive having improved copper corrosion properties



United States Patent LUBRICATING OIL ADDITIVE HAVING IM- PROVED COPPER CORROSION PROPERTIES Julius P. Rocca and Albert C. Henn, Linden, N. J., as-

signors to Esso Research and Engineering Company, a corporation of Delaware No Drawing. Application October 26, 1953, Serial No. 388,442

6 Claims. (Cl. 252--42.7)

This invention relates to phospho-sulfurized metal alkyl phenol sulfides. It is particularly concerned with an improved process for reacting alkaline earth metal alkyl phenol sulfides with a sulfide of phosphorus under conditions whereby a product of reduced corrosiveness to metal surfaces is obtained.

Metal alkyl phenol sulfides and various derivatives thereof are well known as lubricating oil additives for improving the detergency characteristics of lubricating oils employed in internal combustion engines, as anti-oxidants for various organic materials normally susceptible to oxidation and the like. A particularly effective compound of this general type is prepared by reacting a metal alkyl phenol. sulfide with a sulfide of phosphorus to form a phosphorusand sulfur-containing compound having beneficial anti-oxidant characteristics. Such products, disclosed and claimed in U. S. Patent 2,451,345 to J. G. McNab and D. T. Rogers, are extremely effective detergent-inhibitor additives for mineral oil compositions, such as lubricating oil compositions, containing these additives in relatively small amounts. Such products, however, are frequently corrosive to metal surfaces, such as copper surfaces and the like. This corrosiveness results in harm to copper .and other metal parts in the lubrication system of engines. It is a principal object of the present invention to provide an improved process for preparing compounds of the type described having reduced tendency to corrode metal parts and having other improved properties.

In accordance with the present invention, it has been found that the mol ratio of sulfide of phosphorus to metal alkyl phenol sulfide used during the phospho-sulfurization reaction must be maintained below a critical limit of about 0.25:1.0 in order to reduce the corrosive tendencies of the product to acceptable limits. It has further been found that the amount of water present in the reacting mixture is quite critical, amounts above 0.3 weight percent, based on the metal alkyl phenol sulfide, resulting in the formation of anti-corrosive products, largely independent of the ratio of sulfide of phosphorus to metal sulfide employed. Therefore, this invention contemplates a process in which both of these reaction variables are maintained below these critical limits in orderv to produe a final product of reduced corrosivity to metals such as copper.

The improvements obtained in the practice of the present invention, while not fully explainable at this time, are believed to result chiefly from the following factors. The reaction of a sulfide of phosphorus with a metal alkyl phenol sulfide evidently results in the formation of a mixture of mono-, di-, and tri-substituted thiophosphates. The highly substituted thiophosphates are apparently more corrosive to metals than the less substituted derivatives. It appears that maintaining the ratio of reactants below the critical value reduces substantially the Patented Nov. 6, 1956 formation of the corrosive components without deleteriously affecting the potency of the product as an antioxidant additive. With respect to the water content, .it appears that any water, finding its way into the metal alkyl phenol sulfide during neutralization reactions or by other means, reacts with the sulfide of phosphorus, perhaps to form some free sulfur. The free sulfur itself may be corrosive or may in turn react with the metal alkyl phenol sulfide to form highly corrosive components. It is to be understood, however, that it is not desired to be bound by any hypothesisor theoretical considerations regarding the improvements obtained.

in the following examples are described various methods for preparing products in accordance with the prior art and with this invention, and the characteristics of the products so obtained. It is to be understood that these examples are given for illustrative purposes only, and are not to be construed as limiting the scope of the invention in any way.

EXAMPLE 1 A. Preparation of metal alkyl. phenol sulfide barium tert.-octyl phenol sulfide, 4% by weight of Lorol B alcohols (chiefly a mixture of CioC1s alcohols obtained by hydrogenating coconut oil) and 56 weight percent of a mineral lubricating oil fraction was prepared in the following manner: An oil solution containing tert.- octyl phenol sulfide and Lorol B alcohols was heated to a temperature of about C., and barium hydroxide octahydrate was slowly added to the solution with stirring until the phenol was substantially completely neutralized. The alcohols were present during the reaction to reduce the viscosity of the neutralized mixture. The resulting neutralized mixture was then filtered and then blown with nitrogen at a temperature of C. for a period- B. Phospho-sulfurization step A series of laboratory runs were carried out in which portions of the oil concentrate described above (Example 1A) were treated with various quantities of P285. In each case, the reacting component were maintained at a temperature of C. Each batch was soaked at this temperature for two hours, was filtered at this temperature using the flow filter aid, and was then blown with nitrogen for two hours while cooling to ambient temperatures.

Each of the resulting products was analyzed and tested for copper strip corrosion and water sensitivity. Copper strip corrosion tests were the conventional AST M tests in which 5.0 weight percent of the additive to be tested in a standard mineral oil solution is heated in the presence of a clean copper strip for three hours at a temperature of 212 F. The strip is then rated on an arbitrary scale. requirements; Fail means that corrosion is too severe to be tolerated.

The products were also tested for water sensitivity, i. e., the tendency of the additive to separate from the oil in the presence of water. This test is conducted by emulsifying 600 cc. of an oil blend containing 5.0 weight percent of the additive with 1% water by means of a motordriven egg beater-type mixer operated at maximum speed for 15 minutes. After stirring, 500 ccs. of the emulsion is poured into a 500 cc. graduated cylinderand allowed to stand for 24 hours.

Pass means that the product meets specification At the end of this period the centrations of water. Each portion of the oil concentratrate was then treated with P285 under identical conditions 3 amount of emulsion layer separated from the oil is noted. The smaller the amount of separation the better the water resistant quality of the additive. (0.23 mol ratio Pzsszmetal alkyl phenol sulfide, 150 C.

Pertinent data obtained in the laboratory runs are reaction temperature and 4.0 hours reaction and soaking shown in Table I below: 5 time). The resulting products were then tested for copper TABLE I Product analyses and inspections Mol ratio,

Run No. Wt. per- Pis metal cent P28. sulfide Wt. per- Wt. per- Wt. per- S/Ba Copper Water cent Ba cent S cent P ratio strip sens,

corr. cc/500 cc.

3. 50 0. 22 8. 95 5. 58 0. 92 0. 625 Pass- T1. 3. 75 0. 235 8. 93 5. 70 1. 04 0. 639 d0- Tr. 4. 00 0. 25 8. 90 5. 82 1. 0. 653 Fail- 5 4. 50 0.28 8. 95 5.96 1. 19 0.668 d0 8 5. 50 0. 34 8. 71 6. 29 1. 37 0. 720 do 30 6. 00 0. 37 8. 39 6. 92 1. 54 O. 830 do.. 45

It is noted that the copper strip corrosion of the product increased as the molar ratio of P255 to metal sulfide instnp corrosion The results are shownmTablembelow' creased. At a ratio of below 0.25 1.0, a satisfactory TABLE III copper strip corrosion, meeting specification requirements,

was obtained. Much more severe corrosion was observed I gfggfif; 533 00pm.

at higher molar ratios. Run N0. at 140C., phenol sul- Strip It was also found that the water sensitivity of the prodhours w if gig i'it common uct reached undesirably high levels as PzS5:metal sulfide ratio exceeded 0.25:1.0. 7' 0 M0 Pm.

EXAMPLE 2 DZL A series of plant runs were carried out under conditions substantially the same as those employed in the laboratory runs of Example 1. The oil solution of metal At a Wa C nt nt Of a ut 0.3 Weight percent or less, alkyl phenol sulfide used in these runs wa prepared by satisfactory copper strip corrosions were obtained. At the same procedure described in Example 1A, and conhigher water concentrations, corrosive products were obtained in each case about 0.2% Water. The mol ratio tained. of P385 to metal phenol sulfide in the plant runs Was The metal alkyl phenol sulfides to be treated in accarefully controlled at constant levels ranging from 0.22 cordance with the present invention may be selected from to 0.25: 1.0. Reaction times, temperatures and the like any of the suitable, preferably oil-soluble, compounds well were maintained at constant conditions identical to those known to the art. Such compounds are generally predescribed in Example 1B. The reaction conditions and pared by converting the phenol sulfide to a metal salt by tests of the products are shown in Table II below: treatment with a metal or metallic oxide, hydroxide, sul- 1 After addition of barium hydroxide.

TABLE II Product analyses and inspections Mol ratio,

Run No. Wt. perlast: metal cent P185 sulfide Wt. per- Wt. per- Wt. per- S/Ba Copper Water cent Ba cent S cent P ratio strip sens.,

corr. 00/500 cc.

3 5 0. 2 8. 73 5. 70 1. 04 0. 648 PaSS Tr. 3 6 0. 23 8. 68 5. 38 0. 97 0. 620 d0 5 4 0 0 2 8. 56 5.86 1. 09 0. 682 Fall- 12 These runs confirm the results obtained in the laborafide and the like. The alkyl phenol sulfides for example tory studies in showing that a critical increase in corrosivity may have the following typical formula: occurs at molar ratios of 0.25 1.0 and above.

EXAMPLE 3 ED-G An oil solution of barium tert.-octy1 phenol sulfide was prepared substantially in accordance with a prowhere R represents at least one alkyl radical attached to the nucleus, the total number of carbon atoms in all of cedure described in Example 1A with the exception that the neutralized and filtered product, after addition of such radicals attached to each benzene nucleus being at leastfive when the compound is to be dissolved in hydrobarium hydroxide octahydrate, was used as such or was blown with nitrogen at an elevatedtemperature for various lengths of timeto obtain products containing varying concarbon oils, M is a metal, preferably a divalent metal of group II of the periodic table, and x is an integer from 1 to 4.

It should be understood that the above general formulas include compounds in which various substituent atoms or groups may be attached to the aromatic nucleus such as alkyl, cycloalkyl, aralkyl, aryl, carboxyl, hydroxyl, alkoxy, aroxy, sulfhydryl, nitro, ester (organic and/ or inorganic), keto, amino, aldehyde, chlormethyl, aminomethyl, alkyl thiomethyl', alkyl xanthomethyl, metal substituted carboxyl, metal substituted sulfo, metal substituted hydroxyl or sulfhydryl groups, halogen atoms, etc. Different types of atoms or groups may be attached to the same aromatic nucleus.

Alkyl radicals attached to the nucleus may have a total of five to twenty-five carbon atoms in all of such groups, and in some cases as many as sixteen to twenty or more carbon atoms in a single group, as in a wax chain group, or in a plurality of groups, may be preferred. If more than one alkyl group is present in a single molecule, whether or not attached to the same aryl nucleus, such groups may be alike or different. Such alkyl or other hydrocarbon groups may contain substituent groups, such as those named above as substituents in the aromatic nucleus. The various groups or atoms attached to the aromatic nucleus may be in any positions relative to one another.

Suitable metal derivatives of these compounds include the calcium, barium and strontium salts. Other polyvalent metal salts may be used. Typical suitable compounds include calcium tert.-octyl phenol sulfide; barium 2,4-di-tert.-amyl phenol sulfide; strontiun1-tert.-amyl phenol sulfide; mixed calcium-barium tert.-octyl phenol sulfide; and the like.

The metal salts are preferably formed by adding the suitable metal-containing agent to a mineral oil solution or other solution of the phenol sulfide at an elevated temperature. Such neutralization procedures are well known to the art.

After the metal phenol sulfide salt has been formed, it will generally contain a substantial amount of water present in the neutralizing agent or formed during the neutralizing step. This water should be substantially completely removed by a suitable drying step, and in the preferred embodiment of this invention the water content is reduced to below 0.3 weight percent based on the sulfide-containing material. Thus, for example, the alkyl phenol sulfide, or its solution in the solvent medium in which it was formed, may be blown with nitrogen or other suitable inert gas at an elevated temperature above about 100 C., such as about 120 to 200 C. for one to ten or more hours until the water content has been reduced to the desirably low level. Periodic analysis of the material may be carried out to determine when the critical low water content has been obtained.

Good results are usually obtained in preparing such salts in mineral oil if a minor proportion of a higher alcohol, such as stearyl, lauryl, or cetyl alcohol, wool fat alcohol, alcohol prepared by hydrogenating coconut oil and the like is added to the reaction mixture in which the metal salts are prepared. This alcohol reduces foaming during the step of adding the metal reagent, reduces the viscosity of the reacting solution, and acts as an auxiliary solvent for the final product. The best results are obtained by adding a sufiicient quantity of alcohol to give a concentration of about 2 to about 15% based on the final additive concentrate. The alcohol is not deleterious to the final reaction product even though it will react with the sulfide of phosphorus in the subsequent treating step to be explained below.

In treating the metal salt with the sulfide of phosphorus, a suitable sulfide of phosphorus such as P285, P483, P487 or the like, preferably P255 is added to the metal salt or mineral oil solution thereof. The proportions of reactants will be selected such that the mol ratio of sulfide of phosphorus to metal phenol sulfide is below 0.25: 1.0, and preferably above 0.10: 10' tov obtain a product having potent anti-oxidantproperties. In the range of about 0.15: 1.0 to 0.23:1.0 is'generally preferred. Such- The mixture of reactants is preferably heated together at a temperature in,the;range-.of. about to 200"C'.',

preferably to C., to complete the reaction, the period of heating generally being at least about 10 minutes and preferably at least one hour. The reaction is preferably carried out in the presence of a solvent such as a mineral oil in which the metal salt was prepared although other relatively high boiling hydrocarbon solvents such as xylol may be used. The advantage of the mineral lubricating oil base stock as a solvent derives from the fact that the final product may be conveniently shipped or stored as a concentrate in this solvent and then blended with lubricating oil base stocks in the desired concentration to form a finished lubricating oil blend.

After the reaction with the sulfide of phosphorus has been completed, the product may be filtered, if desired, and blown with nitrogen for a suitable time period at an elevated temperature such as about l00-120 C. Other after-treating steps may be used to form a product relatively free of unreacted substances and undesirable side reaction products.

The additives of the present invention are most advantageously blended with mineral oil base stocks in concentrations between the approximate limits of 0.02% and 10.0% by weight, preferably from about 0.1% to 4% by weight being useful. The exact amount of addition agent required for maximum improvement will depend to a certain extent on the particular products used, the nature of the mineral oil base stock and general operating conditions of the engine in which the lubricant is to be employed.

The additives are particularly useful in combinations with alkaline earth metal petroleum sulfonates of the oil-soluble variety to form improved detergent additives for lubricating oils. Other types of additives such as pour point depressers, viscosity index improvers, thickening agents and the like may be used in conjunction with the additives of the present invention.

The additives of the present invention may be used in various lubricating oil base stocks derived from petroleum distillates and residuals refined byconventional means. Hydrogenated oils or white oils may be employed as well as synthetic oils prepared by polymerization of olefins, by reaction of oxides of carbon with hydrogen, or by hydrogenation of coal. The products may also be employed in the synthetic polyether and polyester-type lubricants and the like as such or blended with mineral lubricants. The lubricants will usually range from about 35 to 150 seconds (Saybolt) at 210 F. In addition to being employed in lubricants, the additives of the present invention may also be used in other mineral oil products such as motor fuels, heating oils, hydraulic fluids, cutting oils, turbine oils, transformer oils, gear lubricants, greases and the like. They may also be employed in asphalts, road oils, waxes, fatty oils of animal or vegetable origin, soaps and plastics. They may be also used in natural and synthetic rubber compounds both as vulcanization systems and anti-oxidants, and generally they may be used in any organic materials subject to deterioration by atmospheric oxygen.

What is claimed is:

1. In the process in which an oil-soluble sulfur and phosphorus-containing product having antioxidant properties in the presence of organic materials is formed by reacting together a metal alkyl phenol sulfide and P255 at a temperature in the range of about 100 to 200 C., the improvement for reducing the tendency of the product to corrode metals which comprises utilizing a metal 8 i 5. A process as in claim 4 wherein said alkaline earth metal alltyl phenol sulfide is tert.-octyl phenol sulfide.

' 6. A process as in claim 5 wherein said solvent is a mineral lubricating oil;

- References Cited in the fileof this patent V UNITED STATES PATENTS r 2,451,345 McNab et a1. Oct. 12, 1948 

1. IN THE PROCESS IN WHICH AN OIL-SOLUBLE SULFUR AND PHOSPHORUS-CONTAINING PRODUCT HAVING ANTIOXIDANT PROPERTIES IN THE PRESENCE OF ORGANIC MATERIALS IS FORMED BY REACTING TOGETHER A METAL ALKYL PHENOL SULFIDE AND P2S5 AT A TEMPERATURE IN THE RANGE OF ABOUT 100* TO 200* C., THE IMPROVEMENT FOR REDUCING THE TENDENCY OF THE PRODUCT TO CORRODE METALS WHICH COMPRISES UTILIZING A METAL PHENOL SULFIDE WHICH CONTAINS LESS THAN ABOUT 0.3 WEIGHT PERCENT WATER AND A MOL RATION OF P2S5 TO SAID METAL PHENOL SULFIDE BELOW 0.25:1.0. 